Liquid crystal display devices have advantages such as light weight, thinness, and low power consumption, and are utilized not only for large-size television sets but also as small-sized display devices, e.g., display sections of mobile phones.
A liquid crystal display device includes a liquid crystal display panel, a backlight device, circuitry and a power supply for supplying various electrical signals to the liquid crystal display panel, and a housing which accommodates these. The liquid crystal display panel has a displaying region in which a plurality of pixels are arrayed, and a frame region around it.
The displaying region (active area) of a generic liquid crystal display panel includes pixel electrodes, thin film transistors (TFTs), and the like provided therein, in which images, videos, or the like are displayed. In the frame region are provided: a sealing portion at which substrates are attached together so that a liquid crystal material is sealed in between the substrates; connection lines connected to the gate electrodes and source electrodes of the TFTs; terminals for connection with external driving circuits which input signal/scanning voltages; and so on. In the present specification, any region in which connection lines to the gate electrodes and source electrodes of TFTs, terminals for connection with external driving circuits which input signal/scanning voltages, and the like are located may be referred to as a connection region. In order to prevent deteriorations in display quality at the outer periphery of the active area due to leakage of light from the backlight, disorderly alignment of liquid crystal molecules, and so on, a black mask (light-shielding member) is usually provided in the frame region. Thus, the frame region is a region not contributing to displaying (invalid displaying portion). While liquid crystal display panels are becoming narrower and narrower in their frames each year, it is difficult to eliminate the frame region.
Now, limitations as to how narrow a frame region 85a of a generic liquid crystal display panel (e.g., a TN (Twisted Nematic) type liquid crystal panel) 500 can be will be described with reference to FIG. 11(a) and FIG. 11(b). FIG. 11(a) is a schematic plan view of the liquid crystal display panel 500, and FIG. 11(b) is a schematic cross-sectional view of an α portion shown in FIG. 11(a).
The liquid crystal display panel 500 has a displaying region 85 and a frame region 85a located at the periphery of the displaying region 85. A plurality of pixel electrodes 4 are formed in the displaying region 85 of the liquid crystal display panel 500. The frame region 85a is a region which does not contribute to displaying. In the frame region 85a of the liquid crystal display panel 500, a sealing portion 99 is formed so as to surround the liquid crystal layer 1. The width Ds of the frame region 85a is expressed as a sum of the width D1 of the sealing portion 99 and the distance D2 between the sealing portion 99 and a pixel electrode 4 which is adjacent to the sealing portion 99. The sealing portion 99 is formed by using a dispenser apparatus, a screen printer, or the like to apply a sealant on a substrate so as to constitute a predetermined pattern, and, after this is attached to the other substrate, curing the sealant. The final width D1 of the sealing portion 99 is about 1 mm or more.
Patent Document 1 discloses a method in which a pair of substrates are attached together via a sealant that is applied so as to constitute a predetermined pattern, and thereafter the substrates are cut up, together with the sealant, to thereby produce a plurality of liquid crystal display panels. In the disclosed method, the width D1 of the sealing portion 99 is made about 1 mm or less. According to the method disclosed in Patent Document 1, although the width of the sealing portion 99 can be made about 1 mm or less, making the width D1 of the sealing portion 99 too thin would result in an inadequate strength which induces an insufficiency in that the sealing portion 99 may peel off under a high temperature and high humidity. The above insufficiency will become especially outstanding when the width D1 of the sealing portion 99 is about 0.5 mm or less, and thus the sealing portion 99 of the liquid crystal display panel which is currently mass-produced by the Applicants has a width greater than 0.5 mm.
Next, the reason why it is difficult for the frame region 85a of the liquid crystal display panel 500 to have a width Ds of about 0.5 mm or less will be described.
In the liquid crystal display panel 500, the distance D2 which is needed to maintain the alignment of the liquid crystal material contained in the liquid crystal layer 1 is about 0.2 mm or more. When the distance D2 is less than about 0.2 mm, the liquid crystal material alignment will become disorderly due to the influence of the sealing portion 99, thus causing poor displaying such as a lowered contrast ratio. This means that, in order for the frame region 85a to have a width Ds of about 0.5 mm or less, the width D1 of the sealing portion 99 needs to be about 0.3 mm or less. On the other hand, if the width D1 of the sealing portion 99 is about 0.1 mm or less, the sealing portion 99 will peel off due to inadequate strength, thus causing poor displaying. When the precision of a dispenser apparatus used for forming the sealing portion 99 is taken into consideration, it is very difficult to control the width D1 of the sealing portion 99 to about 0.2 mm to 0.3 mm with a good production yield.
On the other hand, Patent Document 2 discloses a liquid crystal display panel having a polymer dispersed liquid crystal (PDLC) layer in which a curable vinyl compound is used. Patent Document 2 states that forming a polymer dispersed liquid crystal layer from a curable vinyl compound provides an effect of adhesively bonding the pair of substrates, without even forming the sealing portion 99 which would belong to the liquid crystal display panel 500.